In a mobile network, a user equipment (UE) communicates with a core wireless network through a radio access network. In technical specifications provided by 3GPP, a UE is defined as a device providing user access to network services. It corresponds to a mobile station defined in GSM. Under certain circumstances, it is necessary to bar some UEs in a mobile network from accessing a radio access network, for example, to prevent overloading the network, to control congestion, to deal an emergency situation, or to handle a network failure such as Public Land Mobile Network (PLMN) failure, etc.
In an exemplary scenario in which the network discovers that there is congestion, e.g. in a random access channel, the network starts to restrict certain UEs that are configured with the access barring feature from performing a random access procedure so that the UE is effectively barred from accessing the network. The network broadcasts updated access barring information to indicate which UEs are barred from accessing the network. Since access barring information is often included in system information, the network notifies the UEs of the change in the system information by paging. Similarly, when the network congestion is alleviated, the network removes the access restrictions to allow the UEs to access the network again. The network modifies the access barring information in the system information and pages the UEs about the updated access barring information.
Different standards provide different access control mechanisms. In UTRAN standards, access control is achieved through access class barring (ACB). An access class is a random number allocated to each UE and is usually stored in the UE's SIM/USIM (Subscriber Identity Module/Universal Subscriber identity Module) card. There are ten normal access classes, ranging from 0 to 9. A special access class can range from 11 to 15. Access classes are used to identify which portion of the mobile terminals are allowed or disallowed to access the network at certain time. For example, access attempts by UEs belonging to class 0, 1, and 2 may be limited whereas UEs belong to classes 3-9 are allowed to access the network. For another example, access attempts by UEs belonging to a normal access class may be limited whereas access attempts by UEs belonging to a special access class may be allowed. In UTRAN standards, to inform the mobile terminals of the allowed/disallowed access classes, a bitmap indicating which access classes are barred and which are not may be broadcast by the network.
In E-UTRAN standards, the ACB mechanism is implemented using an access barring factor and an access barring time, both of which are broadcast in the system information (SI) when access class barring is in effect.
The updated bitmap or system information is broadcast to every UE. A paging message may be used to notify each device of the updated SI information. For example, when access restrictions have been removed, the affected UEs will be notified of the change via paging messages. In some standards, a UE may be further notified of an upcoming paging message via a paging indicator.
In the present application herein, the term “paging notification” may be used to refer to either a paging message or a paging indication or other equivalent notification signals that provide notifications to UEs of certain upcoming events.
If the UEs, upon being notified of the removal of access restrictions, attempt to access the network all at the same time, the access network may be overloaded by the number of access attempts. The overloading situation is more manifest in an access network in which a large number of Machine Type Communications (MTC) devices are deployed.
MTC devices are devices that generate delay-tolerant and/or low-priority traffic, therefore are more tolerant of access restrictions. MTC devices are often configured to support Extended Access Barring (EAB). EAB is a special access barring mechanism that allows a network operator to restrict access attempts originated from devices configured to support EAB. Network overloads caused by access attempts from MTC devices after EAB access restrictions have been removed are more common than network overloads caused by other ACB access restrictions, partly due to the large number of MTC devices deployed.
Improved methods and apparatus are needed for reducing overloads in access network caused by access attempts from UEs.